From the Professors Foglio:Oh, incidentally — YES, KLAUS IS A CONSTRUCT, NO REALLY, HE IS, TAKE OUR WORD FOR THIS. PLEASE.
Klaus was not heard from at all during the years when the Other was active. Many people whisper that Klaus himself was the Other and the devastating attacks were a hideous revenge directed at the Heterodynes. Klaus returned only after the Other’s attacks had ceased, and he returned in a very bad mood. His early idealism had vanished and his new strategy was simple. He drew a circle on the map and declared everything within it his territory. Every year the circle grew. Aside from a few basic rules, things were to stay the same. The ruling Sparks would stay in power, but no hostilities whatsoever were allowed. Any breach of this Peace was met with ruthless conquest and the swift removal of the aggressors. At first no one took this very seriously, and many of the Gifted rose to challenge Klaus. He wound up in control of much of Europe in just a few years.
Even though he stopped the fighting, Klaus is not popular. The surviving Great Houses want their power back, and the common people believe him to be responsible for the ruin of the Heterodynes. In stories, folksongs and plays, Klaus is usually portrayed as a traitor, always as a villain. Few people bother to point out that it speaks well for his rule that no retaliation is ever made for such amusements.
Even though they dislike and fear him, the people know that the Baron’s Peace will most likely only last as long as Klaus himself. On account of this, there are many wishes for his continued good health—at least until the Heterodynes return.